1. Field of the Invention
The present invention relates to a strip line cross circuit and, more particularly, to an improvement of a circuit for crossing strip lines on a multilayer printed circuit employed in, for example, portable equipment such as a portable telephone set.
2. Description of the Prior Art
Generally, multilayer printed circuit boards have been employed in high-frequency circuits of portable telephone sets. A multilayer printed circuit board can be provided with mounting patterns on the upper and lower surfaces and wiring patterns on inner layers, which has contributed greatly to making the size of the high-frequency circuit smaller (Japanese Patent Unexamined Publication Nos. Sho 63-308999 and Hei 3-129895).
In such a multilayer printed circuit board, when strip lines are placed across each other, a two-level crossing is required wherein the lines are crossed with a space so that they are not coupled electromagnetically with each other.
FIG. 1 schematically shows a conventional cross circuit of inner layer strip lines. When two lines 101 and 102 are crossed on a certain layer L1, the line 101 is connected to a line 105 on a different layer L2 by through holes 103 and 104 so that one line is not coupled to the other, as shown in the figure. That is, in the conventional cross circuit, there was adopted a two-level crossing structure wherein one line 101 bypasses the other line 102 to a lower or upper layer.
Such a conventional structure, however, causes the increased number of layers of a multilayer printed circuit board and the decreased wiring area on the lower layer L2. Moreover, since one inner layer strip line is arranged up and down over two or more layers, the route becomes complicated and the wiring difficult.
It is, accordingly, an object of the present invention to provide a cross circuit which is capable of facilitating the wiring of a multilayer printed circuit and reducing the number of layers.